Integrated Process For Steam Cracking

ABSTRACT

This invention relates to a process and system for cracking hydrocarbon feedstock containing vacuum resid comprising: (a) subjecting a vacuum resid to a first thermal conversion in a thermal conversion reactor (such as delayed coker, fluid coker, Flexicoker™, visbreaker and catalytic hydrovisbreaker) where at least 30 wt % of the vacuum resid is converted to material boiling below 1050° F. (566° C.); (b) introducing said thermally converted resid to a vapor/liquid separator, said separator being integrated into a steam cracking furnace, to form a vapor phase and liquid phase; (c) passing said vapor phase to the radiant furnace in said steam cracking furnace; and (d) recovering at least 30 wt % olefins from the material exiting the radiant furnace (based upon the weight of the total hydrocarbon material exiting the radiant furnace).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed application U.S. Ser.No. ______ (Attorney Docket Number 20010EM008). This application alsorelates to U.S. Ser. No. 12/692,222, filed Jan. 22, 1010.

FIELD OF THE INVENTION

The invention relates to a method of making olefins from a crude orresid-containing crude fraction in a steam cracking furnace or apyrolysis furnace.

BACKGROUND OF THE INVENTION

Thermal cracking of hydrocarbons is a petrochemical process that iswidely used to produce olefins such as ethylene, propylene, butylenes,butadiene, and aromatics such as benzene, toluene, and xylenes. Each ofthese is a valuable commercial product in its own right. For instance,the olefins may be oligomerized (e.g., to form lubricant basestocks),polymerized (e.g., to form polyethylene, polypropylene, and otherplastics), and/or functionalized (e.g., to form acids, alcohols,aldehydes and the like), all of which have well-known intermediateand/or end uses.

Steam cracking, also referred to as pyrolysis, has long been used tocrack various hydrocarbon feedstocks into olefins, preferably lightolefins such as ethylene, propylene, and butenes. Typically, thefeedstock for steam cracking is a hydrocarbon such as naphtha, gas oil,or other non-resid containing fractions of whole crude oil, which may beobtained, for instance, by distilling or otherwise fractionating wholecrude oil. Conventional steam cracking utilizes a steam cracking furnacewhich has two main sections: a convection section and a radiant section.The hydrocarbon feedstock typically enters the convection section of thefurnace as a liquid (except for light feedstocks which enter as a vapor)wherein it is typically heated and vaporized by indirect contact withhot flue gas from the radiant section and by direct contact with steam.The vaporized feedstock (and optional steam) mixture is then conveyedinto the radiant section where the cracking takes place. Typically thevaporized mixture is introduced through crossover piping into theradiant section where it is quickly heated, at pressures typicallyranging from about 10 to about 50 psig (69 to 345 kPa), to a severehydrocarbon cracking temperature, such as in the range of from about1450° F. (788° C.) to about 1650° F. (900° C.), to provide thoroughthermal cracking of the feedstream. The resulting products, includingolefins, leave the steam cracking furnace for further downstreamprocessing.

After cracking, the effluent from the pyrolysis furnace contains avariety gaseous hydrocarbons, e.g., saturated, monounsaturated, andpolyunsaturated, and can be aliphatic and/or aromatic, as well assignificant amounts of molecular hydrogen. The cracked product is thenfurther processed such as in the olefin production plant to produce, asproducts of the plant, the various separate individual streams of highpurity, i.e., hydrogen, the light olefins ethylene, propylene,butylenes, and aromatic compounds, as well as other products such aspyrolysis gasoline.

As worldwide demand for light olefins increases and the availability offavorable crude sources is depleted, it becomes necessary to utilizeheavier crudes (i.e., those having higher proportions of resid), whichrequires increased capital investments to process and handle therefining byproducts. It is highly desirable to have processes that cantake lower cost, heavier crudes, and produce a more favorable productmix of light olefins, more efficiently. However, conventional steamcracking processes are known to be prone to severe fouling by feedstockscontaining even small concentrations of resid, which is commonly presentin low quality, heavy feeds. Thus, most steam cracking furnaces arelimited to processing of higher quality feedstocks which have hadsubstantially all of the resid fraction removed in other refineryprocesses. Such additional processes increase the cost of the overallprocess. Likewise, removal of the resid fraction lowers the overallconversion efficiency of the refinery process, since most of the residfraction is mixed with low value fuel oils, rather than being convertedto higher-value materials.

U.S. Patent Published Patent Application No. 2007/0090018, incorporatedherein by reference, discloses integration of hydroprocessing and steamcracking. A feed comprising crude or resid-containing fraction thereofis severely hydrotreated and passed to a steam cracker to obtain anolefins product.

Cracking of heavy hydrocarbon feeds in fluidized cokers has beendescribed. For example, U.S. Pat. No. 3,671,424, incorporated herein byreference, discloses a two-stage fluid coking process in which the firststage is a transfer line for short contact time and the second is eithera transfer line or a fluidized bed.

The use of knock-out drums integrated with the steam cracking furnacehas evolved as an important extension of this platform to enableprocessing of heavier feedstocks such as atmospheric resids. Theknock-out drum provides a means to separate the heaviest components fromcrackable gas oil molecules and prevent the heaviest, asphaltene-typemolecule containing fractions from fouling the steam cracking furnace.Unfortunately, by using this approach, most of the heavy vacuum residmolecules, which are favored as feedstock due to lower cost, remain inthe liquid phase and are not converted in the radiant section of thesteam cracking furnace.

Other patents of interest include U.S. Pat. No. 7,097,758; U.S. Pat. No.7,138,047; U.S. Pat. No. 7,193,123; U.S. Pat. No. 3,487,006; U.S. Pat.No. 3,617,493; U.S. Pat. No. 4,257,871; U.S. Pat. No. 4,065,379; U.S.Pat. No. 4,180,453; U.S. Pat. No. 4,210,520; U.S. Pat. No. 3,898,299;U.S. Pat. No. 5,024,751; U.S. Pat. No. 5,413,702; U.S. Pat. No.6,210,561; U.S. Pat. No. 7,220,887; US 2007/023845; WO 01/66672; WO2007/117920; U.S. Pat. No. 6,632,351; U.S. Pat. No. 4,975,181; WO2009/025640; US 2007/0090018 and WO 2007/117919. Other references ofinterest include: “Tutorial: Delayed Coking Fundamentals.” P. J. Ellisand C. A. Paul, paper 29a, Topical Conference on Refinery Processing,1998 Great Lakes Carbon Corporation (which can be downloaded fromhttp://www.coking.com/DECOKTUT.pdf).

There remains in the art a need for new means and improved processes foreconomical processing of heavy, resid-containing feeds for theproduction of olefins, aromatics, and other valuable petrochemicalproducts. Likewise there remains a need in the art for means to upgraderesid to a more useful and/or efficient composition.

This invention discloses a method for producing chemicals from heavyfeedstocks in a manner where significant portions of the vacuum residare converted to lighter molecules which can be more easily vaporized inthe knock-out drum and subsequently converted to fuels and chemicals.

SUMMARY OF THE INVENTION

This invention relates to a process for cracking hydrocarbon feedstockcontaining resid comprising:

(a) passing a vacuum resid containing hydrocarbon feedstock to a firstthermal conversion zone, where the feedstock is heated to a temperatureof less than 649° C. (1200° F.), where at least 30 wt % of the vacuumresid is converted to material boiling below 566° C. (1050° F.);(b) introducing said thermally converted resid to a vapor/liquidseparator (such as a knock-out drum), said separator being in fluidcommunication with (e.g., integrated into) a steam cracking furnace, toform a vapor phase and liquid phase;(c) passing said vapor phase to the radiant furnace in said steamcracking furnace; and(d) recovering at least 30 wt % olefins from the material exiting theradiant furnace (based upon the weight of the total hydrocarbon materialexiting the radiant furnace).

In another embodiment, this invention relates to a process for crackinghydrocarbon feedstock containing resid comprising:

(a) heating a hydrocarbon feedstock containing resid;

(b) passing said heated hydrocarbon feedstock to vapor/liquid separator(such as a knock-out drum);

(c) flashing said heated hydrocarbon feedstock in said separator to forma vapor phase and a liquid phase containing said resid;

(d) passing at least a portion of said resid-containing liquid phasefrom said separator to a thermal conversion reactor operating below 649°C. (1200° F.), and optionally containing coke particles;

(e) passing said thermally converted resid-containing liquid phase to avapor/liquid separator (such as a knock-out drum), said separator beingin fluid communication with (e.g., integrated into) a steam crackingfurnace, to form a second vapor phase and second liquid phase;

(f) passing said second vapor phase to the radiant furnace in said steamcracking furnace; and

(g) recovering at least 30 wt % olefins from the material exiting theradiant furnace (based upon the weight of the total hydrocarbon materialexiting the radiant furnace).

In another embodiment, the liquid phase exiting the first vapor/liquidseparator is further heated to a temperature such as 1000 to 1200° F.(538-649° C.), typically in the lower coils of the convection section ofa steam cracker, typically a portion of the heated material typically isvisbroken, thereafter water (such as steam) is used to quench andvaporize the visbroken materials the reaction, the vaporized visbrokenmaterial is then passed to a second vapor/liquid separator where thevisbroken material is separated into a liquid phase and a vapor phase.The vapor phase is then introduced into a steam cracker (either in theconvection section or the radiant section) and where at least 30 wt %olefins are recovered from the material exiting the radiant furnace(based upon the weight of the total hydrocarbon material exiting theradiant furnace).

Advantageously, the initial hydrocarbon feedstock typically containsbetween 10 wt % and 50 wt % of resid boiling at 566° C.⁺, preferablyabout 20-40 wt %, and the process described herein enables a highfraction of this resid to be converted to chemicals.

In a preferred embodiment, the resid containing liquid from the secondvapor/liquid separator is not processed further for producing chemicals.Instead this material is preferably used as a blendstock into fuel oilor for further refinery processing for producing fuels.

In a preferred embodiment this invention relates to a process forcracking hydrocarbon feedstock containing vacuum resid comprising:

(a) heating a hydrocarbon feedstock containing at least 1 wt % vacuumresid, based upon the weight of the hydrocarbon feedstock, andconverting at least 10 wt % of the vacuum resid to material boilingbelow 566° C.;

(b) passing said heated hydrocarbon feedstock to a vapor/liquidseparator (preferably the liquid bottoms phase from the vapor/liquidseparator is heated to a temperature of 593 to 649° C.);

(c) flashing said heated hydrocarbon feedstock in said separator to forma vapor phase and a liquid phase containing said resid;

(d) passing at least a portion of said resid-containing liquid phasefrom said separator to a first thermal conversion zone (preferablycontaining coke particles, preferably the zone has a coke particle/freshfeed ratio (wt/wt) of at least 1:1 (preferably at least 3:1, preferablyat least 5:1, alternately from 1:1 to 50:1, preferably from 3:1 to30:1), based on the weight of circulating coke solids and fresh feedentering the zone) to thermally convert at least a portion of saidresid-containing liquid phase;

(e) passing said thermally converted liquid phase to a vapor/liquidseparator, said separator being in fluid communication with a steamcracking furnace, to form a second vapor phase and second liquid phase;

(f) passing said second vapor phase to said steam cracking furnace tothermally convert at least a portion of said second vapor phase(alternately the second vapor phase can be used as fuel or blendstock);and

(g) recovering at least 30 wt % olefins from the material exiting theradiant furnace of said steam cracking furnace (based upon the weight ofthe total hydrocarbon material exiting the radiant furnace).

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures below, similar apparatuses and/or process steps areidentified with like numbers.

FIG. 1 is a flow diagram of an embodiment of the present inventionprocess.

FIG. 2 is a flow diagram of an embodiment of the present inventionprocess.

FIG. 3 is a flow diagram of an embodiment of the present inventionprocess.

FIG. 4 is a flow diagram of an embodiment of the present inventionprocess.

DETAILED DESCRIPTION OF THE INVENTION

This invention involves integration of a heavy feed steam crackerincluding an integrated vacuum resid vapor/liquid separator (e.g.,knock-out drum) with a thermal conversion unit, such as a delayed coker,fluid coker, Flexicoker™, visbreaker, or catalytic hydrovisbreaker,where vacuum resid is converted to lighter components that are suitablefor steam cracking (“Suitable for steam cracking” means that thematerials can be cracked in a steam cracker.) By closely integrating thetwo conversion processes, the overall process is able to efficientlyconvert a much wider range of heavy feeds to high value chemicals whileminimizing fouling. For purposes of this invention a steam crackingfurnace (also referred to as a “steam cracker”) is a pyrolysis furnacethat has two main sections or furnaces: a convection section and aradiant section, where hydrocarbon feedstock enters the less severeconvection section of the furnace as a liquid (except for lightfeedstocks which enter as a vapor) and where the feedstock is heated andvaporized typically by indirect contact with hot flue gas from theradiant section and is optionally contacted with steam. The vaporizedfeedstock and steam mixture is then conveyed into the radiant sectionwhere it is quickly heated, at pressures typically ranging from about 10to about 50 psig (69 to 345 kPa-gauge), to a severe hydrocarbon crackingtemperature, such as in the range of from about 1450° F. (788° C.) toabout 1650° F. (900° C.), to provide thorough thermal cracking of thefeedstream. The resulting products typically comprise olefins, aromaticsand dienes.

Resid as used herein refers to the complex mixture of heavy petroleumcompounds otherwise known in the art as residuum or residual.Atmospheric resid is the bottoms product produced in atmosphericdistillation when the endpoint of the heaviest distilled product isnominally 650° F. (343° C.), and is referred to as 650° F.⁺ (343° C.⁺)resid. Vacuum resid is the bottoms product from a column under vacuumwhen the heaviest distilled product is nominally 1050° F. (566° C.), andis referred to as 1050° F.⁺ (566° C.⁺) resid. (The term “nominally”means here that reasonable experts may disagree on the exact cut pointfor these terms, but probably by no more than +/−50° F. or at most+/−100° F.) This 1050° F.⁺ (566° C.⁺) portion contains asphaltenes,which traditionally are considered to be problematic to the steamcracker, resulting in severe fouling and potentially corrosion orerosion of the apparatus. The term “resid” as used herein means the 650°F.⁺ (343° C.⁺) resid and 1050° F.⁺ (566° C.⁺) resid unless otherwisespecified; note that 650° F.⁺ resid comprises 1050° F.⁺ resid. Accordingto this invention, at least a portion of the 650° F.⁺ resid, up to atleast the 1050° F.⁺ boiling point fraction, is vaporized, such as whencombined with steam, and/or when the pressure is reduced or flashed inthe knock-out drum of the steam cracker. The terms “vacuum residcontaining hydrocarbon feedstock”, “atmospheric resid containinghydrocarbon feedstock”, “resid containing hydrocarbon feedstock” and thelike, mean that the identified resid is present at least 0.1 wt %, basedupon the weight of the hydrocarbon feedstock (preferably at least 1 wt%, preferably at least 10 wt %, preferably at least 15 wt %, preferablyat least 20 wt %).

The terms “flash drum”, “flash pot”, “knock-out drum” and knock-out pot”are used interchangeably herein; they are known in the art, meaninggenerally, a vessel or system to separate a liquid phase from a vaporphase (a “vapor/liquid separator”). The term “flash” means generally toeffect a phase change for at least a portion of the material in thevessel from liquid to vapor, via a reduction in pressure and/or anincrease in temperature. An integrated knock-out drum is a vapor/liquidseparator that is in fluid communication with a steam cracker.Specifically, the integrated knock-out drum is in fluid communicationwith the convection section of a steam cracker, where feedstock isheated (optionally mixed with superheated steam) and transferred to saidknock-out drum operating as a vapor/liquid separator, thereafter thevapors from the knock-out drum are returned to the steam cracker,preferably either to the convection or radiant section, or both. Theaddition of steam may further assist flash separation by reducing thehydrocarbon partial pressure, assist in conversion and vaporization ofthe 750° F.⁺ (399° C.⁺) to 1050° F.⁺ (566° C.⁺) (preferably even asubstantial portion of the 1100° F.⁺ (593° C.⁺)) resid fractions, andprevent fouling.

The preferred flash drums or vapor/liquid separation devices, and theirintegration with pyrolysis units have previously been described in U.S.Pat. Nos. 7,090,765, 7,097,758, and 7,138,047, which are incorporatedherein by reference. Another apparatus effective as a flash drum forpurposes of the present invention is described in U.S. Pat. No.6,632,351 as a “vapor/liquid separator”.

The vapor/liquid separator operates at a temperature and pressure wherethose portions of the feed material that cause coking are kept in aliquid state, preferably operates at a temperature of between about 375to 525° C., preferably from 400 to 500° C., preferably from 800° F.(about 425° C.) and about 870° F. (about 465° C.), but also typicallynot over about 900° F. (about 482° C.).

According to the invention a crude oil or fraction thereof containingresid is utilized as a feedstock for a steam cracking furnace. Suitablelower value feeds may typically include heavier crudes, defined as thosehydrocarbon feedstocks that have a low API gravity as a result of highconcentrations of 650° F.⁺ (343° C.⁺) resid, high sulfur, high TotalAcid Number (TAN), high naphthenes, high aromatics, and/or low hydrogencontent.

Crude, as used herein, means whole crude oil as it issues from awellhead, production field facility, transportation facility, or otherinitial field processing facility, optionally including crude that hasbeen processed by a step of desalting, treating, and/or other steps asmay be necessary to render it acceptable for conventional distillationin a refinery. Crude as used herein is presumed to contain resid.

Crude fractions are typically obtained from the refinery pipestill.Although any crude fraction obtained from the refinery pipestill may beuseful in the present invention, a significant advantage offered by thepresent invention is that crude or crude fractions still containing allor a portion of the original 1050° F.⁺ (566° C.⁺) resid present in thewhole crude obtained from the wellhead may be used as feed for a steamcracker. In one embodiment, the crude or other feedstock to the presentsystem may comprise at least about 1 wt % 1050° F.⁺ (566° C.⁺) resid,preferably at least about 5 wt % 1050° F.⁺ (566° C.⁺) resid, and morepreferably at least about 10 wt % 1050° F.⁺ (566° C.⁺) resid up to about50 wt % 1050° F.⁺ (566° C.⁺) resid.

Resid typically contains a high proportion of undesirable impuritiessuch as metals, sulfur, and nitrogen, as well as high molecular weight(C₁₂ ⁺) naphthenic acids (measured in terms of TAN according to ASTMD-664, TAN refers to a total acid number expressed as milligrams (“mg”)of KOH per gram (“g”) of sample). Yet another advantage of the presentinvention is that feeds high in one or more of these impurities may bereadily processed. In some embodiments, this invention can be practicedon 566° C.⁺ resid having: one or more (preferably two, three, four,five, six or seven) of the following properties: 1) 50 ppm of Ni ormore, alternately 100 ppm or more, alternately 125 ppm or more, basedupon the weight of the 566° C.⁺ resid; and/or 2) 200 ppm vanadium ormore, alternately 500 ppm or more, alternately 900 ppm or more, basedupon the weight of the 566° C.⁺ resid; and/or 3) 4 wt % sulfur or more,alternately 5 wt % or more, alternately 6 wt % or more, based upon theweight of the 566° C.⁺ resid; and/or 4) a TAN of at least 0.1,alternately at least 0.3, alternately from about 0.1 to about 20, about0.3 to about 10, or about 0.4 to about 5; and/or 5) an API gravity of 19or less (ASTM D6822, 15.5° C.); and/or 6) a C₅ asphaltenes content of atleast 0.04 grams of C₅ asphaltenes per gram of resid (“C₅ asphaltenes”refers to asphaltenes that are insoluble in pentane as determined byASTM Method D2007); and/or 7) a kinematic viscosity at 37.8° C. of atleast 10 cSt (as determined by ASTM D445). Example resids that can beused herein are the 566° C.⁺ resids obtained from crudes including, butnot limited to, crudes from of the following regions of the world: U.S.Gulf Coast, southern California, north slope of Alaska, Canada tarsands, Canadian Alberta region, Mexico Bay of Campeche, Argentinean SanJorge basin, Brazilian Santos and Campos basins, Egyptian Gulf of Suez,Chad, United Kingdom North Sea, Angola Offshore, China Bohai Bay, ChinaKaramay, Iraq Zagros, Kazakhstan Caspian, Nigeria Offshore, Madagascarnorthwest, Oman, Netherlands Schoonebek, Venezuelan Zulia, Malaysia, andIndonesia Sumatra. Additional resids useful herein include 566⁺° C.⁺resids obtained from crude oils described as “disadvantaged” in U.S.Pat. No. 7,678,264, incorporated by reference herein.

In a preferred embodiment, wherein the feed comprises crude oratmospheric resid that contain appreciable amounts of 1050° F.⁺ (566°C.⁺) resid, e.g., 10 wt % or more of 1050° F.⁺ (566° C.⁺) resid, or 20wt % or more of 1050° F.⁺ (566° C.⁺) resid, or 30 wt % or more of 1050°F.⁺ (566° C.⁺) resid, or 40 wt % or more of 1050° F.⁺ (566° C.⁺) resid,or even up to 50 wt % of 1050° F.⁺ (566° C.⁺) resid, theresid-containing feed is passed into a first steam cracking furnace withintegrated knock-out drum.

Bottoms from a first knock-out drum are then passed into a thermalconversion unit such as a delayed coker, fluid coker, Flexicoker™,visbreaker or catalytic hydrovisbreaker, where it is heated and at least30 wt % (based upon the weight of the feed) of the vacuum resid isconverted to a 1050° F.⁻ (566° C.⁻) cut. As used herein a 1050° F.⁻(566° C.⁻) cut is defined to be hydrocarbons normally boiling below1050° F.⁻ (566° C.⁻). The thermally converted resid is introduced to aknock-out drum, said drum being integrated into a steam crackingfurnace, to form an overhead vapor phase and liquid bottoms phase. Saidvapor phase is passed to the radiant furnace in said steam crackingfurnace. At least 30 wt % olefins are recovered from the materialexiting the radiant furnace (based upon the weight of the totalhydrocarbon material exiting the radiant furnace). The addition of steammay further assist flash separation by reducing the hydrocarbon partialpressure, assist in conversion and vaporization of the 750° F.⁺ (399°C.⁺) to 1150° F.⁺ (621° C.⁺) resid fractions, and prevent fouling.

The fluid coker preferably includes an integrated air gasifier (orpartial oxidation reactor) which is used to convert coke to fuel gas bysteam/air gasification and combustion at between about 1400-1800° F.(760-982° C.). This gasification can be facilitated by cofeeding oxygenor by using oxygen enriched air. Hot, partially gasified coke from thisgasification reaction is continuously withdrawn from the gasifier andfed to one or more solids transfer lines where it is contacted with thebottoms material recovered from one or more steam cracking furnacesequipped with integrated vapor/liquid separators (such as knock-outdrums). This residual oil fraction is converted at 1300-1800° F.(704-982° C.) to a mixture of lighter hydrocarbons containing highconcentrations of ethylene and propylene. While the transfer linereactors can be configured in several ways, a preferred configuration issimilar to that used in fluid catalytic cracking units; e.g., thetransfer line is operated as a vertical riser reactor where the hotsolids are contacted with feed near the bottom of the riser, the solidsand vapor are transported upward along the riser, and the solids andvapor are separated using one or more cyclones in series. Alternativelythe transfer line can be operated as “downer” or downflow reactor.Irrespective of the specific configuration, the transfer line reactor ishighly effective for contacting hot coke with the residual oil.

Alternatively, vacuum resid from a refinery (already cut out of thecrude) can be passed directly into the resid conversion unit and thenused as feedstock for a steam cracking furnace equipped with anintegrated knock-out drum.

Preferably, the flash drum preferably operates at a temperature of fromabout 800° F. (about 425° C.) and about 870° F. (about 465° C.), butalso typically not over about 900° F. (about 482° C.). Flashing materialthrough the flash drum to obtain an overhead vapor and liquid bottomsfurther facilitates vaporization of the 650° F.⁺ (343° C.⁺) resids.

Steam cracking alone provides for a product comprising significantyields of fuel oil, tar, and SCN (steam cracked naphtha) in addition tothe desired ethylene, propylene, butylenes, C₅ olefins and dienes, andsingle-ring aromatic products. The instant process is particularlyeffective and advantageous for steam cracker integrations because theprocess achieves a much higher level of resid conversion to chemicalswithout fouling and it minimizes the need for cooling and reheating theintermediate product streams.

Liquid products produced in resid thermal cracking can produce highyields of chemicals in the steam cracker and show reduced tendency(versus the 1050° F.⁺ (566° C.⁺) resid) for fouling the steam crackingfurnace.

This invention further relates to a process for producing chemicals fromheavy feedstocks in a manner where more of the vacuum resid is largelyconverted to fuels and chemicals. Generally, the process involvesintegration of a heavy feed steam cracker including an integrated vacuumresid knock-out drum with a secondary thermal conversion reactor wherevacuum resid is converted to lighter components that are suitable forsteam cracking The secondary thermal conversion reactor is normallyoperated in a similar time/temperature window as conventionalvisbreaking and coking processes, although it can be advantageous tooperate at somewhat milder conditions than are normally employed forproducing fuels. In an embodiment, in the processes described herein,the thermal conversion reactor operates at 25° C. or more (alternately50° C. or more, alternately 75° C. or more) below the operatingtemperature of the furnace section of the steam cracker following thethermal conversion reactor. In some embodiments it is preferable tocascade the lighter liquids and gases through the radiant section of thesteam cracker without condensation. By closely integrating the twoconversion processes, one operating at milder severity and one operatingat high severity, the process is able to convert a much wider range ofheavy feeds to high value chemicals. (When a reactor or reaction zone isstated to be “operating at” a certain temperature it means that materialin the reactor or zone has been heated to that temperature.)

In the figures and description below reference to a knock-out drum maybe taken to generally refer to any vapor/liquid separator device.

A basic flow scheme for the process of the invention is shown in FIG. 1,where a hydrocarbon feedstock (containing atmospheric resid) 100 isintroduced to a first thermal conversion reactor 600 where at least 30wt % (preferably at least 50%, preferably at least 70%, preferably about90%) of the resid is converted to a 1050° F.⁻ (566° C.⁻) cut and/orpetroleum coke. The whole liquid and vapor product is then introduced(207) to a knock-out drum 205 (typically operating at 800 to 900° F.(423 to 482° C.)), said drum being in fluid communication with (e.g.,integrated into) a steam cracking furnace 200 (having a convectionfurnace 206 and a radiant furnace 250) to form an overhead vapor phase210 and liquid bottoms phase 220. The vapor phase 210 is then passed tothe radiant furnace 250 in said steam cracking furnace 200, eitherdirectly or via a heater, such a transfer line heater or a convectionsection 206 of the steam cracker 200, where the radiant section istypically operating at 750 to 900° C., and at least 30 wt % (preferably40% or more) of the radiant section feed is converted to light olefins(e.g., C₂, C₃ C₄) which are recovered from the material exiting theradiant furnace 221 (based upon the weight of the total hydrocarbonmaterial exiting the radiant furnace).

Another basic flow scheme for the process of the invention is shown inFIG. 2, where a resid containing hydrocarbon feedstock 100 is heated(typically in the convection furnace 206 of a steam cracker furnace)and, preferably, at least 10 wt % (preferably at least 20 wt %,preferably at least 25 wt %, alternately from about 20-30%) of thevacuum resid is converted to a 1050° F.⁻ (566° C.⁻) cut. The whole feedis heated to about 750-850° F. (399-454° C.). The heated feedstock isthen passed 207 to a knock-out drum 205 (preferably integrated into asteam cracker furnace), typically operating at 800 to 900° F. (423 to482° C.). The heated feedstock is then separated (typically in the flashdrum by centrifugal forces and gravity settling of coalesced liquiddroplets) to form an overhead vapor phase 210 and a liquid bottoms phase220 containing said resid. The liquid bottoms phase 220 is then passedto a thermal conversion reactor 300, optionally containing cokeparticles, where it is more highly converted into lighter molecules 223boiling below 1050° F. (566° C.). The lighter molecules 223 are thenpassed to a knock-out drum 205* (typically operating at 800 to 900° C.),said drum preferably being integrated into a steam cracking furnace, toform a second overhead vapor phase 210* and second liquid bottoms phase220*. The overhead vapor phase 210* is then passed to the radiantfurnace 250* (typically operating at 750 to 900° C.), in a steamcracking furnace, preferably the steam cracking furnace that theknock-out drum 205* is integrated with. Thereafter at least 30 wt %(preferably at least 40% light olefins (e.g., C₂, C₃, C₄ olefins) arerecovered from the material exiting the radiant furnace 225 (based uponthe weight of the total hydrocarbon material exiting the radiantfurnace).

Another basic flow scheme for the process of the invention is shown inFIG. 3. A heavy feedstock crude or vacuum resid 101 (preferablycontaining about 10 to 50% molecules boiling in the vac resid range(1050° F.⁺ (566° C.⁺)) 100 is fed to a first steam cracking furnace 200which includes an integrated knock-out drum 205. The whole feed isheated to about 750-850° F. (399-455° C.) in the convection section 206of the furnace. The whole feed passes 207 into the knock-out drumseparation device 205 where molecules boiling below about 1000-1100° F.(538-593° C.) are vaporized (or remain vaporized) and are separated fromheavier compounds which remain in the liquid phase. Material typicallyenters the drum at a temperature of about 800-850° F. (427-454° C.) andvaporization is facilitated by the use of steam stripping or strippingwith light hydrocarbons. The vapors pass overhead 210 into the radiantsection 250 of the first steam cracking furnace, whereas the heavyliquids are withdrawn from the bottom of the knock-out drum 220. Theheavy liquid molecules are then directed to a secondary conversionreactor 300 where the heavy liquids are thermally cracked into lightermolecules. The light molecules then pass 221 to a drum separation device400 integrated in a steam cracker furnace (not shown) where moleculesboiling below about 538-593° C. are vaporized (or remain vaporized) andare separated from heavier compounds which remain in the liquid phase.Material typically enters the drum at a temperature of about 427-470° C.and vaporization is facilitated by the use of steam stripping orstripping with light hydrocarbons. The vapors pass overhead through line410 into the radiant section (not shown) of a steam cracking furnace,whereas the bottoms are withdrawn from the bottom of the knock-out drumthrough line 420. Steam may be introduced into the steam crackingfurnace (not shown). Bottoms 420 from the knock-out drum may be used forfuel oil, among other things. In a preferred embodiment, the materialexiting the thermal conversion reactor is not reintroduced into thefirst steam cracker.

Preferably heavy liquids from several knock-out drum equipped furnacesare preferably combined to achieve better economy of scale in thesecondary vacuum resid conversion reactor. The secondary conversionreactor can be directly coupled with the steam cracking furnace and cantake the form of a delayed coker drum, a fluid coker, a flexicoker, avisbreaker, a catalytic hydrovisbreaker, or other suitable conversionreactor designs. Optionally, the feed can be further preheated to about800-900° F. (427-482° C.) before entering the coking reactor byreheating in a reboiler or furnace or by contacting with a hot gas suchas steam or hydrogen. In the secondary conversion reactor, a highfraction of the vacuum resid molecules (e.g., above about 50%) arethermally cracked into lighter molecules which boil below 1050° F. (566°C.). Once through conversion of the vacuum, resid molecules are normallyin the range of 30-60% in visbreaking or up to 95% or more in oncethrough catalytic hydrovisbreaking or coking. This is accomplished bybalancing the reaction temperature and residence time with stripping oflighter liquid products in the conversion vessel which is operatedadiabatically. To maintain hydrogen balance at high levels of residconversion or with lower hydrogen content feeds, a significant fractionof the heavy vacuum resid molecules are converted to a solid cokeproduct with low hydrogen content or to heavier tar-like bottomsfractions. In a catalytic hydrovisbreaker, in addition to producing aheavier, tar-like bottoms fraction with low hydrogen content, hydrogenis added to feed heteroatoms to produce H₂S, NH₃, and H₂O and to crackedolefinic fragments to prevent coking. In the delayed coker case, thereaction is continued until the drum gradually fills with solid coke.The feed is then switched to a second drum, while coke is removed fromthe first drum, and the process is continued in a cyclic manner. In apreferred embodiment, vapor and liquid product from the coking reactionare fed to a second steam cracking furnace incorporating an integratedknock-out drum. This furnace may be operated with a slightly lowerknock-out drum temperature or cut point as compared to the first furnace(or group of furnaces used to supply the coker feed), preferably thesecond knock-out drum operates at 25° C. or more (preferably 50° C. ormore, preferably 75° C. or more) below the operating temperature of thefirst knock-out drum. Lighter molecules generated in the coking (orsecondary conversion) reactor remain vaporized and pass into the radiantsection of the steam cracker, whereas the heavier vacuum gas oil (VGO)molecules and material that was not converted in the coker are withdrawnfrom the bottom of the second knock-out drum. In a preferred embodiment,these molecules are disposed by other means, for example blending intofuel oil, and are not recycled back to the coker as is normallypracticed in fuels coking processes. In another preferred embodiment,hot vapor overhead from the coker can be partially quenched using acooler VGO or distillate stream between the outlet of the coker and theinlet of the knock-out drum in order to promote further condensation ofheavier VGO components with lower hydrogen content.

While vacuum resid coking and gas oil steam cracking are well knownprocesses, the integration of a coker with a steam cracking furnaceincluding an integrated knock-out drum is not known. Moreover, it isnormally preferred to operate cokers with bottoms recycle to extinctionto maximize yields of lighter fuel components or fuel feedstocks. Thisbottom recycle operation produces highly refractory compounds, such asheptane insoluble polynuclear aromatics hydrocarbons, which are notsuitable for chemical feeds. Particularly unsuitable feedstocks aremolecules containing four or more condensed aromatic rings. Fuel cokersare normally equipped with a large primary fractionator which is used topreheat fresh feed by mixing with coker products and to scrub the cokervapor of entrained liquid droplets by mixing coker feedstock with thecoker drum vapor stream. Bottoms reenter the reactor with this freshfeed. In the integrated steam cracking process, this primaryfractionator is eliminated.

In the practice of this invention, the integrated knock-out drum isparticularly efficient and effective with regards to the operation ofheavy feed steam cracking and coking processes without fouling, as itallows cut points between the vapor and heavy liquids to be easilyvaried consistent with the properties of the feedstock.

A particularly preferred configuration is the direct integration of athermal cracking process with a steam cracker. By direct integration ismeant that that the steam cracker convection section heats the feed tothe thermal conversion device and the effluent of the thermal conversiondevice passes directly to the knock-out drum and then to the radiantsection without passing through any intermediate heat exchangers.

Preferred thermal conversion reactors for use herein include delayedcokers, fluid cokers, Flexicokers™, visbreakers and catalytichydrovisbreakers.

A preferred basic configuration for the thermal conversion reactor issimilar to a delayed coker. Specifically the process: i) operates at aslightly lower severity (e.g., from 800 to 900° F. (427-482° C.),preferably 800 to 850° F. (427-454° C.), ii) uses about 0.1 to 1.0 kg ofsteam per kg of resid feedstock, iii) operates coke drums at lowerhydrocarbon vapor partial pressures and/or shorter vapor residencetimes, iv) separates coking vapors from entrained heavy liquids in anintegrated knock-out drum device, and v) preferably operates oncethrough without bottoms recycle. Delayed coking is described in anarticle by P. J. Ellis and C. A. Paul entitled “Tutorial: Delayed CokingFundamentals.” paper 29a, Topical Conference on Refinery Processing,1998 Great Lakes Carbon Corporation (which can be downloaded fromhttp://www.coking.com/DECOKTUT.pdf). In a delayed coker, the productvapors and entrained liquids are heat exchanged with colder feed bydirect contact in a drum that functions as a distillation tower. Thisdrum typically operates at close to 50 psig (345 kPa). This techniqueresults in an extinction recycle of heavy coker liquids resulting incomplete conversion to vapors exiting the drum serving as thedistillation tower and coke accumulating in the coke drums. Thepreheated liquid feed exiting the bottom of the drum serving as adistillation tower and heat exchanger is typically at 360 to 400° C.This hot liquid is passed through a pump which raises the liquidpressure to 300 to 600 psig (2.1 to 4.1 MPa). The hot pressurized feedflows through the coker furnace where it is heated to close to 500° C.The furnace effluent close to 500° C. and 60 psig (414 kPa) flows intothe coke drum which separates solid coke from vapors and entrainedliquid droplets. The volatile components can then be removed and passedto steam cracker (preferably a steam cracker having an integratedknock-out drum), leaving coke behind. The material passed to the steamcracker is then converted into olefins.

In another embodiment, the liquid phase from the first vapor/liquidseparator is heated in a heating zone (such as a delayed coker) tocoking temperatures (such as up to 649° C.) and is then conducted to acoking zone wherein volatiles are collected overhead and coke is formed.Preferably the liquid phase from the first vapor/liquid separator issubjected to delayed coking which involves the thermal decomposition ofpetroleum resid to produce gas, liquid streams of various boilingranges, and coke. In the delayed coking process, the liquid phase fromthe first vapor/liquid separator is rapidly heated in a fired heater ortubular furnace, then the heated liquid phase from the firstvapor/liquid separator is then passed to a coking drum that ismaintained at conditions under which coking occurs, generally attemperatures above about 400° C. under super-atmospheric pressures. Theheated feed in the coker drum also forms volatile components that areremoved and passed to steam cracker (preferably a steam cracker havingan integrated knock-out drum), leaving coke behind. The material passedto the steam cracker is then converted into olefins.

If a catalytic hydrovisbreaking reactor is used as the thermalconversion reactor 300, the heavy oil is mixed with catalyst (such as ametal sulfide) and a molecular hydrogen-containing gas (e.g., H₂,syngas, fuel gas) and a high fraction of the vacuum resid molecules,such as at least about 60%, even between about 60-80%, or even up to95%, are converted into lighter molecules which boil below 1050° F.(566° C.). Typical operating conditions include temperatures of 785-900°F. (418-482° C.), residence times of 2-100 minutes (0.1 to 5 LHSV(Liquid Hourly Space Velocity)), hydrogen treat rates of 500-5000 SCF/B,and operating pressures of 100-3000 psig (0.689-20.7 MPa). Preferredconditions are about 785-860° F. (418-460° C.), 10-40 min (0.2 to 2LHSV), 1000-2500 SCF/B, and 500-1500 psig (3.45-17.2 MPa). Typicalreactor designs include a coil reactor, a coil reactor combined with apumparound soaker, or a slurry bubble column with liquids recirculation,although other designs are possible. In general, the reaction conditionsare optimized to match feed quality; e.g., lower quality feeds mayrequire more severe conditions to achieve high conversions in the rangeof 50-95%, preferably about 60-80%. Conventional facilities (high andlow pressure separators) are used to remove vapor and liquid productsafter the reactor and to recycle unused hydrogen to the process.Catalysts used in the catalytic hydrovisbreaking process are normallybased on sulfided transition metals. The most common metals are Mo, Ni,and Co. When the process is operated as a slurry, catalysts are normallybased on micrometer or sub micrometer sized metal sulfide particlesdispersed in a carbonaceous matrix (a.k.a Microcat®). The Microcat® canbe based on molybdenum sulfide; other transition metal sulfides such asthose produced from tungsten, vanadium, iron, nickel, and cobalt; ormolybdenum sulfide in combination with one or more of these alternativetransition metal sulfides, or combinations of the alternative transitionmetal sulfides. While molybdenum alone provides satisfactory operationsfor many feeds, use of other metals or multimetallic catalyst systemscan provide improved performance for resid conversion, hydrogenaddition, and desulfurization, e.g., higher catalytic activity. Freshcatalyst is typically formed by mixing a heavy VGO cut with a low costcatalyst precursor such as ammonium heptamolybdate or phosphomolybdicacid and heating to 600-800° F. (316-427° C.) for 10-60 minutes.Catalyst pre-forming is preferably carried out in the presence ofhydrogen and H₂S or elemental sulfur. The Microcat® produced in thismanner is stable over many cycles of conversion, filtration, and reuse.However, the catalyst can deactivate over long times. For this reason,it may be advantageous to remove a small purge stream from the process.This “spent” catalyst can be regenerated in separate facilities orreformulated into fresh catalyst precursor. When the process is operatedin a fixed bed, conventional fixed bed catalysts commonly used for fixedbed resid hydrodesulfurization (the production of low sulfur fuel oilfrom feeds comprising 650+ resid), FCC feed pretreatment, and heavy feedhydrocrackers are employed.

The Flexicoking™ processes useful herein were developed by Exxon in the1960s and are described in detail in a wide range of previous patents aswell as textbooks on resid processing technologies. For example, U.S.Pat. No. 3,671,424, incorporated herein by reference, describes andillustrates a suitable fluidized coking apparatus and process for useherein.

In another embodiment, the liquid phase exiting the first vapor/liquidseparator is further heated to a temperature such as 1000 to 1200° F.(538 to 649° C.), preferably 1100 to 1200° F. (593 to 649° C.),preferably about 1125 to 1190° F. (607 to 643° C.), typically in thelower coils of the convection section of a steam cracker, wheretypically a portion of the heated material typically is visbroken,thereafter water (such as steam) is used to quench and vaporize thevisbroken materials. The vaporized visbroken material is then passed toa second vapor/liquid separator where the visbroken material isseparated into a second liquid phase and a second vapor phase. Thesecond vapor phase is then introduced into a steam cracker (either inthe convection section or the radiant section, or both) and at least 30wt % olefins (preferably 40% or more, preferably 50 wt % or more) arerecovered from the material exiting the radiant furnace (based upon theweight of the total hydrocarbon material exiting the radiant furnace).

Generally, kinetic and heat of reaction calculations show that almostcomplete visbreaking conversion is attained when resids are exposed to1200° F. (649° C.) for roughly 2 seconds. But because visbreaking is anendothermic reaction, just heating rapidly to 1200° F. (649° C.) is notsufficient. During the subsequent visbreaking, the resid cools to suchan extent that roughly 60% conversion of 950° F.⁺ (510° C.⁺) to 950° F.⁻(510° C.⁻) occurs. Higher temperatures increase visbreaking conversion,but secondary coking reactions also occur. Thus, in a preferredembodiment, the bottoms from the first knock-out drum are heated to1000-1200° F. (538 to 649° C.) (preferably from 1100 to 1200° F. (593 to649° C.), preferably to about 1200° F. (649° C.)) rapidly in the lowerconvection section where flue heat continually replaces endothermic heatlosses. To minimize fouling in the convection section the bottoms areheated in only one pass so that the high velocity of the residcontinually washes coke precursors off of the internal surfaces. If somecoking does occur, periodic steam/air decoking will burn/spall it offthe tubes.

In an alternate embodiment, the convection tubes can be porous sinteredmetal surrounded by a solid outside tube where steam is in the annulus.The steam pressure is higher than the process pressure causing steam toseep though the sintered inner tube preventing coke laydown.

The visbroken bottoms (e.g., 1000-1200° F. (538 to 649° C.)) are thenquenched rapidly upon exiting the convection section otherwise the extraresidence time may cause excessive coking. Steam and/or water areexcellent quench mediums because they reduce the hydrocarbon partialpressure vaporizing a significant fraction of the newly formed lighthydrocarbons. Note, during this quenching operation ample liquid ispresent, which prevents coking In the vapor phase, two-molecule cokingreactions are not favored (than the liquid phase) because thehydrocarbon concentration is low. In a preferred embodiment, any foulingthat may still occur in the vapor phase is prevented by quenching to˜840° F. (449° C.). In an optional embodiment, a portion of the bottomsfrom the primary knock-out drum can aid in the quenching operations.

In another embodiment, a small second knock-out drum separates visbrokenlight-hydrocarbons from remaining resid. Like the first knock-out drum,the piping to the second drum coalesces the remaining liquid, which thenseparates from the hydrocarbon vapor/steam mixture in the drum. Byoperating the second drum at ˜840° F. (449° C.) fouling in the vaporphase will be low. Thus, the vapor can be conveyed either to the firstknock-out drum or to the first drum's overhead piping. Alternatively,the vapor/liquid from the quench can be directed to the piping upstreamof the first knock-out drum eliminating the need for a second knock-outdrum. Further a dual knock-out drum design allows the bottoms from thefirst knock-out drum to be severely visbroken just once, reducing thelikelihood of severe coking Note, the secondary knock-out drumtemperature is not so high (nor the hydrocarbon partial pressure so low)that the bottoms will not flow and/or can not be fluxed.

Steam tracing typically further reduces vapor phase fouling. Coker testsshow that superheating coke gas to as high as 1250° F. (677° C.)minimizes fouling in cyclones, presumably by prevent liquid depositionthe primary coking mechanism. Thus, a preferred embodiment of thepresent invention is to prevent liquid deposition by steam tracing withsuperheated steam all vessels and lines downstream of the vapor/liquidseparations. The tracing steam, which is significantly hotter than theprocess vapor, eliminates cold spots that may exist if these lines areonly insulated. Even hotter steam can be used to superheat the vapor toa limited extent. If necessary, some of the tracing steam can beinjected directly into the vapor to providing further superheating.

A significant advantage of the present invention is high utilization ofheavy feeds without excessive coking

Another basic flow scheme for the process of the invention is shown inFIG. 4. A heavy feedstock crude or resid 101 (preferably containingabout 10 to 50% molecules boiling in the vac resid range (1050° F.⁺(566° C.⁺)) is fed to a first steam cracking furnace 200 which includesan integrated knock-out drum 205. The whole feed is heated to about 800to 900° F. (427 to 482° C.) in the convection section 206 of thefurnace. The whole preheated feed 207 passes into the knock-out drumseparation device 205 where molecules boiling below about 1000-1100° F.(538-593° C.) are vaporized (or remain vaporized) and are separated fromheavier compounds which remain in the liquid phase. Material typicallyenters the drum at a temperature of about 800-850° F. (427-454° C.) andvaporization is facilitated by the use of steam stripping or strippingwith light hydrocarbons. The vapors pass 210 into the radiant section250 of the first steam cracking furnace, whereas the heavy liquids arewithdrawn from the bottom of the knock-out drum 220. The heavy liquidmolecules are then directed to the convection section 206 of the furnace(either by mixing with fresh feed or passing into a separate heatingcoil zone) where the heavy liquids are visbroken into lighter molecules.Water or steam 227 is introduced to vaporize the lighter molecules(typically outside the convection section). The visbroken lightmolecules then pass 221 to a knock-out drum separation device 400integrated in a steam cracker furnace (not shown) where moleculesboiling below about 538-593° C. are vaporized (or remain vaporized) andare separated from heavier compounds which remain in the liquid phase.The vapors pass 410 into the radiant section (not shown) of a steamcracking furnace, whereas the bottoms are withdrawn from the bottom ofthe knock-out drum through line 420. Steam may be introduced into thesteam cracking furnace (not shown). Bottoms 420 from the knock-out drummay be used for fuel oil, among other things. In a preferred embodiment,the material exiting the thermal conversion reactor is not reintroducedinto the first steam cracker.

In a preferred embodiment, the residual vacuum resid material remainingafter primary conversion and separation in the knock-out drum is notrecycled for additional conversion to chemicals. This residual materialcontains highly refractory compounds, such as heptane insolublepolynuclear aromatics hydrocarbons, which are not preferred for chemicalfeeds. These residual molecules are better utilized by blending intofuel oil or optionally by converting in separate refinery residconversion equipment to produce fuels.

In another embodiment, the vacuum resid feed converted in this inventioncontains greater than 10.0 wt % hydrogen, preferably greater than 11.0wt %.

In another embodiment, the feed into the thermal conversion reaction(such as a coker or delayed coker) contains greater than 10.0 wt %hydrogen, preferably greater than 11.0 wt %, preferably greater than11.5 wt %, based upon the weight of the feed.

In another embodiment, the temperature of the gas exiting the thermalconversion reactor (such as a coker or delayed coker) is 750 to 900° F.(399 to 482° C.), preferably 780 to 860° F. (416 to 460° C.), preferably800 to 850° F. (427 to 454° C.). In another embodiment, the pressure inthe thermal conversion reactor is up to 30 psig (207 kPa), preferably upto 25 psig (172 kPa), preferably from 1 to 20 psig (138 kPa).

In a preferred embodiment, the hydrocarbon feedstock is not cooled whenpassing from the convection section of the first steam cracking furnaceto the integrated first knock-out drum. By not cooled is meant that themixed flow of feedstock liquid and vapor preferably does not drop intemperature by more than 30° C. (alternately by not more than 50° C.,alternately by not more than 100° C.). Likewise in another embodiment,the hydrocarbon feedstock is not cooled when passing from the convectionsection of the second steam cracking furnace to the integrated secondknock-out drum.

In another embodiment of the processes described herein the thermallyconverted material (such as resid or liquid bottoms phase) is passed tothe convection section of a steam cracker prior to entering theintegrated knock-out drum.

In another embodiment, molecular hydrogen (typically a molecularhydrogen containing gas) is added to the heated feedstock at any pointin the process.

In another embodiment, steam can be added to the heated feedstock at anypoint in the process. This can be especially useful to assistvaporization in the integrated knock-out drum zones.

In a particularly preferred embodiment, the thermal conversion reactoroperates at 649° C. or less, preferably 640° C. or less, preferably 630°C. or less.

In a particularly preferred embodiment, the thermal conversion reactoris a delayed coker operating with low severity conditions (e.g.,temperature less than 860° F. (460° C.) and pressure of 30 kPa or less)and the output from the delayed coker is transferred directly into aknock-out drum, preferably the output from the delayed coker istransferred to a knock-out drum integrated into a steam cracker (theoutput from the delayed coker may be put through the convection sectionof the steam cracker before it is transferred to the integratedknock-out drum). In this scheme, the feed to the delayed coker is heatedin the convection section of the steam cracker and the effluent from thedelayed coker drum flows directly in the knock-out pot that isintegrated with the steam cracker radiant section. A given coke drum canbe integrated to supply feed to one or more steam cracker furnacesequipped with integrated knock-out drums. Integration of a multiple cokedrums with one or more furnaces and knock-out pots is also possible.Instead of one drum, there could be two or three drums in parallel. Onedrum would be on stream and the others would be being emptied of coke.

In a particularly preferred embodiment, vacuum resid is passed into asteam cracker convection section, then passed to a vapor/liquidseparator (where the vapor/liquid separator is in fluid communicationwith the steam cracker, particularly the convection section of the steamcracker), thereafter the resid is converted into a vapor phase and aliquid phase. The vapor phase is passed into the same or different steamcracker in the radiant or convection section, or both. The liquid phaseis passed to a thermal conversion zone, such as a coker, delayed coker,flexicoker, catalytic visbreaker or a catalytic hydrovisbreaker, whereit is converted into a vapor or liquid stream and coke. The vapor orliquid stream then passed into the convection section of a steam cracker(preferably a steam cracker different from the first steam cracker) andthereafter passed to a vapor/liquid separator (where the vapor/liquidseparator is in fluid communication with the steam cracker, particularlythe convection section of the steam cracker), and thereafter the heatedvapor or liquid stream is converted into a vapor phase and a liquidphase and said vapor phase is passed into the same or different steamcracker in the radiant or convection section, or both.

In another embodiment, this invention relates to:

1. A process for cracking hydrocarbon feedstock containing vacuum residcomprising:(a) passing a vacuum resid containing hydrocarbon feedstock to a firstthermal conversion zone where the feedstock is heated to a temperatureof less than 649° C. (e.g. operating at less than 649° C.), where atleast 30 wt % of the vacuum resid is converted to material boiling below566° C.;(b) introducing said thermally converted resid to a vapor/liquidseparator, said separator being in fluid communication with a steamcracking furnace, to form a vapor phase and liquid phase;(c) passing said vapor phase to said steam cracking furnace; and(d) recovering at least 30 wt % olefins from the material exiting theradiant furnace of the steam cracking furnace (based upon the weight ofthe total hydrocarbon material exiting the radiant furnace).2. The process of paragraph 1, wherein the liquid bottoms phase from thevapor/liquid separator of step (b): is brought (e.g. heated or cooled)to a temperature of 538 to 649° C. (alternately, less than 649° C.) tovisbreak at least a portion of the liquid bottoms phase; thereafter thevisbroken liquid bottoms phase is quenched and subsequently passed to asecond vapor/liquid separator, where the visbroken liquid bottoms phaseis separated into a second liquid phase and a second vapor phase;thereafter the second vapor phase is then introduced into the steamcracking furnace of step (c).3. A process for cracking hydrocarbon feedstock containing vacuum residcomprising:

(a) heating a hydrocarbon feedstock containing vacuum resid andconverting at least 10 wt % of the vacuum resid to material boilingbelow 566° C.;

(b) passing said heated hydrocarbon feedstock to a vapor/liquidseparator;

(c) flashing said heated hydrocarbon feedstock in said separator to forma vapor phase and a liquid phase containing said resid;

(d) passing at least a portion of said resid-containing liquid phasefrom said separator to a first thermal conversion zone;

(e) passing said thermally converted liquid phase to a vapor/liquidseparator, said separator being in fluid communication with a steamcracking furnace, to form a second vapor phase and second liquid phase;

(f) passing said second vapor phase to said steam cracking furnace tothermally convert (at least a portion of) said second vapor phase; and

(g) recovering at least 30 wt % olefins from the material exiting theradiant furnace of said steam cracking furnace (based upon the weight ofthe total hydrocarbon material exiting the radiant furnace).

4. The process of paragraph 3, wherein the liquid phase from step (c):is heated to a temperature of 538 to 649° C. to visbreak at least aportion of the liquid phase; thereafter the visbroken liquid phase isquenched and subsequently passed to a another vapor/liquid separator,where the visbroken liquid phase is separated into a visbroken liquidphase and a visbroken vapor phase; thereafter the visbroken vapor phaseis then introduced into the thermal conversion zone of step (d).5. The process of any of paragraphs 1 to 4, wherein the liquid bottomsphase in claim 1 from the vapor/liquid separator of step (b) in claim 1or the or the liquid phase from step (c) in claim 2 is heated to atemperature of 593 to 649° C.6. The process of any of paragraphs 1 to 5, wherein the thermalconversion zone contains coke particles, where the zone has a cokeparticle/fresh feed ratio (wt/wt) of at least 1:1 (preferably at least3:1, preferably at least 5:1, alternately from 1:1 to 50:1, preferablyfrom 3:1 to 30:1), based on the weight of circulating coke solids andfresh feed entering the zone.7. The process of any of paragraphs 1 to 5, wherein the thermalconversion zone is a delayed coker, a fluid coker, a Flexicoker™, avisbreaker or a catalytic hydrovisbreaker.8. The process of any of paragraphs 1 to 5, wherein the thermalconversion zone is a delayed coker.9. The process of any of paragraphs 1 to 8, wherein the thermalconversion zone operates at 25° C. or more below the operatingtemperature of the furnace section of the steam cracker following thethermal conversion zone.10. The process of any of paragraphs 1 to 9, wherein the vacuum residfeed contains greater than 10.0 wt % hydrogen.11. The process of any of the above claims, wherein the feed into thethermal conversion zone contains greater than 11.0 wt % hydrogen.12. The process of any of paragraphs 1 to 11, wherein the temperature ofthe gas exiting the thermal conversion zone is 399 to 482° C.13. The process of any of paragraphs 1 to 12, wherein the thermallyconverted resid of claim 1 is passed to the convection section of asteam cracker prior to entering the vapor/liquid separator.14. The process of any of paragraphs 2 to 13, wherein thermallyconverted liquid phase of claim 2 is passed to the convection section ofa steam cracker prior to entering the vapor/liquid separator.15. The process of any of paragraphs 1 to 14, wherein hydrogen or steamis added to the heated feedstock at any point in the process.16. The process of any of paragraphs 1 to 15, wherein the steam crackerconvection section heats the feed to the thermal conversion zone and theeffluent of the thermal conversion zone passes directly to thevapor/liquid separator and then to the radiant section of the steamcracker without passing through any intermediate heat exchangers.17. The process of any of paragraphs 1 to 16, wherein at least 40 wt %olefins are recovered from the material exiting the radiant furnace(based upon the weight of the total hydrocarbon material exiting theradiant furnace).18. The process of any of paragraphs 1 to 17, wherein the first thermalconversion zone is a fluid coker.19. The process of any of paragraphs 1 to 18, wherein the first thermalconversion zone is a catalytic hydrovisbreaker.20. The process of any of paragraphs 1 to 19, wherein the first thermalconversion zone is a hydrovisbreaker operating at a temperature of 400to less than 649° C.21. A system for cracking hydrocarbon feedstock containing vacuum residcomprising:

a) a first thermal conversion zone operating at a temperature of lessthan 649° C. selected from the group consisting of: a delayed coker, afluid coker, a Flexicoker™, a visbreaker or a catalytic hydrovisbreaker,said first thermal conversion zone in fluid communication with b) asteam cracking furnace having a vapor/liquid separator in fluidcommunication with said furnace.

22. The system of paragraph 21, further comprising a second avapor/liquid separator in fluid communication with said thermalconversion zone.23. The system of paragraph 21 or 22, wherein the first thermalconversion zone is a fluidized coker comprising:

-   -   i) a fluidized bed gasifier,    -   ii) a transfer line reactor comprising a hydrocarbon feed inlet        in fluid communication with a lower portion of said separator,        and a pyrolysis product outlet line,    -   iii) a solids conduit connecting a lower portion of said        fluidized bed gasifier with said transfer line reactor, and    -   iv) at least one cyclone separator having an inlet connected to        said pyrolysis product outlet line, a cracked product outlet at        a top portion of said cyclone separator, and a solids outlet at        the bottom of said cyclone separator.        24. The system of paragraph 23, further comprising an air/steam        inlet at the bottom of said fluidized bed gasifier.        25. The system of paragraph 23 or 24, wherein said fluidized        coker further comprises a fluidized bed heater vessel, having        recirculating solids conduits connecting lower portions of said        heater vessel and said gasifier, and at least one gas conduit        connected between an upper portion of said gasifier and the        lower portion of said heater vessel.        26. The system of any of paragraphs 23 to 25, wherein said        cyclone separator solids outlet is connected to either or both        of said fluidized bed gasifier or said heater vessel.        27. The system of any of paragraphs 23 to 26, comprising two        solids conduits connecting lower portions of said heater vessel        and said gasifier.        28. The system of any of paragraphs 23 to 27, wherein said        transfer line reactor is a vertical riser reactor, wherein said        solids conduit and said hydrocarbon feed inlet are connected to        a lower portion of said reactor.        29. The system of any of paragraphs 23 to 28, wherein said        transfer line reactor is a downflow reactor wherein said solids        conduit and said hydrocarbon feed inlet are connected to an        upper portion of said reactor.

EXAMPLES

A series of three vacuum resids with variable quality and hydrogencontent were subjected to coking conditions as summarized in Table 1.The coking conditions were chosen to be milder in severity than normalpractice in order to maximize 1050° F.⁻ cut liquid products with reducedlight gas production. Products from the coking reaction were analyzed todetermine the yields of naphtha, distillate, and gas oil and todetermine basic liquid product qualities (gravity, hydrogen content,etc).

Steam cracking process simulation models were then used to estimate theyields of chemical products that can be produced from the full boilingrange coker product. Selected steam cracker product yields arehighlighted in Table 2. It can be readily seen that this coking plussteam cracking process enables production of a high yield of chemicalproducts from the vacuum resid including ethylene, propylene, andbutenes. High olefin yields are favored when the starting vacuum residhas a higher hydrogen content in the range of 11-12 wt % or more. Yieldsof heavy, lower value tar and gas oil products increase as the feedhydrogen content decreases.

TABLE 1 Mild Severity Coking of Vacuum Resids with Variable QualityInitial Vacuum Resid Feed A B C API* 5.4 9.8 16.5 % H 10.18 11.21 12.16Conditions Unit pressure psig (kPa)   3 (20.7)   20 (137.9)   20 (137.9)Avg Temp of Coke 820 (438) 800 (427) 824 (440) Bed ° F. (° C.) Yield wt% H₂S 0.58 0.68 0.20 Methane 2.10 2.08 1.77 Other C4⁻ 4.10 4.90 5.20Naphtha 11.61 15.75 18.83 (C5⁻, 400° F. (204° C.)) Distillate 19.6721.53 23.69 (400° F.-650° F. (204-343° C.)) Bottom (650° F.⁺ 38.38 24.3817.41 (343° C.)) Coke 23.57 24.38 17.41 Hydrogen Content Naphtha (400°F.⁻ 13.7 14.1 14.2 (204° C.⁻)) Distillate 12.5 12.64 13.2 (400° F.-650°F. (204-343° C.)) Bottom (650° F.⁺ 11 11.8 12.3 (343° C.)) *API =American Petroleum Institute gravity in degrees

TABLE 2 Steam Cracking Yields for Wide Cut Coker Liquids Estimated UsingSteam Cracker Process Simulation Model Initial Vacuum Resid Feed A B CAPI 5.4 9.8 16.5 SC Yields wt % Ethylene Plus Propylene Plus 28.4 33.938.6 C4 Yields TAR (C17+) 26.7 18.0 13.9

Unless otherwise specified, the meanings of terms used herein shall taketheir ordinary meaning in the art; reference shall be taken, inparticular, to Handbook of Petroleum Refining Processes, Third Edition,Robert A. Meyers, Editor, McGraw-Hill (2004). In addition, all prioritydocuments, patents, patent applications, test procedures (such as ASTMmethods), and other documents cited herein are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted. Also, when numerical lower limits and numerical upper limitsare listed herein, ranges from any lower limit to any upper limit arecontemplated.

The invention has been described above with reference to numerousembodiments and specific examples. Many variations will suggestthemselves to those skilled in this art in light of the above detaileddescription. All such obvious variations are within the full intendedscope of the appended claims.

1. A process for cracking hydrocarbon feedstock containing vacuum residcomprising: (a) passing a vacuum resid containing hydrocarbon feedstockto a first thermal conversion zone, where the feedstock is heated to atemperature of less than 649° C., where at least 30 wt % of the vacuumresid is converted to material boiling below 566° C.; (b) introducingsaid thermally converted resid to a vapor/liquid separator, saidseparator being in fluid communication with a steam cracking furnace, toform a vapor phase and liquid phase; (c) passing said vapor phase tosaid steam cracking furnace (preferably the radiant furnace in the steamcracking furnace); and (d) recovering at least 30 wt % olefins from thematerial exiting the radiant furnace of the steam cracking furnace(based upon the weight of the total hydrocarbon material exiting theradiant furnace).
 2. The process of claim 1, wherein the liquid bottomsphase from the vapor/liquid separator of step (b): is brought to atemperature of 538 to 649° C. to visbreak at least a portion of theliquid bottoms phase; thereafter the visbroken liquid bottoms phase isquenched and subsequently passed to a second vapor/liquid separator,where the visbroken liquid bottoms phase is separated into a secondliquid phase and a second vapor phase; thereafter the second vapor phaseis then introduced into the steam cracking furnace of step (c).
 3. Theprocess of claim 1, wherein the liquid bottoms phase from thevapor/liquid separator of step (b) is heated to a temperature of 593 to649° C.
 4. The process of claim 1, wherein the thermal conversion zonecontains coke particles, said zone having a coke particle/fresh feedratio (wt/wt) of at least 1:1, based on the weight of circulating cokesolids and fresh feed entering the zone.
 5. The process of claim 1,wherein the thermal conversion zone is a delayed coker, a fluid coker, aFlexicoker™, a visbreaker or a catalytic hydrovisbreaker.
 6. The processof claim 5, wherein the thermal conversion zone is a delayed coker. 7.The process of claim 1, wherein the thermal conversion zone operates at25° C. or more below the operating temperature of the furnace section ofthe steam cracker following the thermal conversion reactor.
 8. Theprocess of claim 1, wherein the vacuum resid feed contains greater than10.0 wt % hydrogen.
 9. The process of claim 1, wherein the feed into thethermal conversion zone contains greater than 11.0 wt % hydrogen. 10.The process of claim 1, wherein the temperature of the gas exiting thethermal conversion zone is 399 to 482° C.
 11. The process of claim 1,wherein the thermally converted resid of claim 1 is passed to theconvection section of a steam cracker prior to entering the vapor/liquidseparator.
 12. The process of claim 1, wherein hydrogen or steam isadded to the heated feedstock at any point in the process.
 13. Theprocess of claim 1, wherein the steam cracker convection section heatsthe feed to the thermal conversion zone and the effluent of the thermalconversion reactor passes directly to the vapor/liquid separator andthen to the radiant section of the steam cracker without passing throughany intermediate heat exchangers.
 14. The process of claim 1, wherein atleast 40 wt % olefins are recovered from the material exiting theradiant furnace (based upon the weight of the total hydrocarbon materialexiting the radiant furnace).
 15. The process of claim 1, wherein thefirst thermal conversion zone is a fluid coker.
 16. The process of claim1, wherein the first thermal conversion zone is a catalytichydrovisbreaker.
 17. The process of claim 1, wherein the first thermalconversion zone is a hydrovisbreaker operating at a temperature of 400to less than 649° C.
 18. A process for cracking hydrocarbon feedstockcontaining vacuum resid comprising: (a) heating a hydrocarbon feedstockcontaining at least 1 wt % vacuum resid, based upon the weight of thehydrocarbon feedstock, and converting at least 10 wt % of the vacuumresid to material boiling below 566° C.; (b) passing said heatedhydrocarbon feedstock to a vapor/liquid separator; (c) flashing saidheated hydrocarbon feedstock in said separator to form a vapor phase anda liquid phase containing said resid; (d) passing at least a portion ofsaid resid-containing liquid phase from said separator to a firstthermal conversion zone to thermally convert at least a portion of saidresid-containing liquid phase; (e) passing said thermally convertedliquid phase to a vapor/liquid separator, said separator being in fluidcommunication with a steam cracking furnace, to form a second vaporphase and second liquid phase; (f) passing said second vapor phase tosaid steam cracking furnace to thermally convert at least a portion ofsaid second vapor phase; and (g) recovering at least 30 wt % olefinsfrom the material exiting the radiant furnace of said steam crackingfurnace (based upon the weight of the total hydrocarbon material exitingthe radiant furnace).
 19. The process of claim 18, wherein the liquidphase from step (c): is heated to a temperature of 538 to 649° C. tovisbreak at least a portion of the liquid phase; thereafter thevisbroken liquid phase is quenched and subsequently passed to a anothervapor/liquid separator, where the visbroken liquid phase is separatedinto a visbroken liquid phase and a visbroken vapor phase; thereafterthe visbroken vapor phase is then introduced into the thermal conversionzone of step (d).
 20. The process of claim 18, wherein the liquidbottoms phase in claim 1 from the vapor/liquid separator of step (b) inclaim 1 or the or the liquid phase from step (c) in claim 2 is heated toa temperature of 593 to 649° C.
 21. The process of claim 18, wherein thethermal conversion zone contains coke particles and the zone has a cokeparticle/fresh feed ratio (wt/wt) of at least 1:1, based on the weightof circulating coke solids and fresh feed entering the zone.
 22. Theprocess of claim 18, wherein the thermal conversion zone is a delayedcoker, a fluid coker, a Flexicoker™, a visbreaker or a catalytichydrovisbreaker.
 23. The process of claim 18, wherein the thermalconversion zone is a delayed coker.
 24. The process of claim 18, whereinthe thermal conversion zone operates at 25° C. or more below theoperating temperature of the furnace section of the steam crackerfollowing the thermal conversion zone.
 25. The process of claim 18,wherein the vacuum resid feed contains greater than 10.0 wt % hydrogen.26. The process of claim 18, wherein the feed into the thermalconversion zone contains greater than 11.0 wt % hydrogen.
 27. Theprocess of claim 18, wherein the temperature of the gas exiting thethermal conversion zone is 399 to 482° C.
 28. The process of claim 18,wherein the thermally converted resid of claim 1 is passed to theconvection section of a steam cracker prior to entering the vapor/liquidseparator.
 29. The process of claim 18, wherein thermally convertedliquid phase of claim 2 is passed to the convection section of a steamcracker prior to entering the vapor/liquid separator.
 30. The process ofclaim 18, wherein hydrogen or steam is added to the heated feedstock atany point in the process.
 31. The process of claim 18, wherein the steamcracker convection section heats the feed to the thermal conversion zoneand the effluent of the thermal conversion zone passes directly to thevapor/liquid separator and then to the radiant section of the steamcracker without passing through any intermediate heat exchangers. 32.The process of claim 18, wherein at least 40 wt % olefins are recoveredfrom the material exiting the radiant furnace (based upon the weight ofthe total hydrocarbon material exiting the radiant furnace).
 33. Theprocess of claim 18, wherein the first thermal conversion zone is afluid coker.
 34. The process of claim 18, wherein the first thermalconversion zone is a catalytic hydrovisbreaker.
 35. The process of claim18, wherein the first thermal conversion zone is a hydrovisbreakeroperating at a temperature of 400 to less than 649° C.
 36. A system forcracking hydrocarbon feedstock containing vacuum resid comprising: a) afirst thermal conversion zone operating at a temperature of less than649° C. selected from the group consisting of: a delayed coker, a fluidcoker, a Flexicoker™, a visbreaker or a catalytic hydrovisbreaker, saidfirst thermal conversion zone in fluid communication with b) a steamcracking furnace having a vapor/liquid separator in fluid communicationwith said furnace.
 37. The system of claim 36, further comprising asecond a vapor/liquid separator in fluid communication with said thermalconversion zone.
 38. The system of claim 36, wherein the first thermalconversion zone is a fluidized coker comprising: i) a fluidized bedgasifier, ii) a transfer line reactor comprising a hydrocarbon feedinlet in fluid communication with a lower portion of said separator, anda pyrolysis product outlet line, iii) a solids conduit connecting alower portion of said fluidized bed gasifier with said transfer linereactor, and iv) at least one cyclone separator having an inletconnected to said pyrolysis product outlet line, a cracked productoutlet at a top portion of said cyclone separator, and a solids outletat the bottom of said cyclone separator.
 39. The system of claim 38,further comprising an air/steam inlet at the bottom of said fluidizedbed gasifier.
 40. The system of claim 38, wherein said fluidized cokerfurther comprises a fluidized bed heater vessel, having recirculatingsolids conduits connecting lower portions of said heater vessel and saidgasifier, and at least one gas conduit connected between an upperportion of said gasifier and the lower portion of said heater vessel.41. The system of claim 38, wherein said cyclone separator solids outletis connected to either or both of said fluidized bed gasifier or saidheater vessel.
 42. The system of claim 38, comprising two solidsconduits connecting lower portions of said heater vessel and saidgasifier.
 43. The system of claim 38, wherein said transfer line reactoris a vertical riser reactor, wherein said solids conduit and saidhydrocarbon feed inlet are connected to a lower portion of said reactor.44. The system claim 38, wherein said transfer line reactor is adownflow reactor wherein said solids conduit and said hydrocarbon feedinlet are connected to an upper portion of said reactor.